Publications

Oxides glasses are suitable for electronic and optoelectronic applications (band gap higher than 3 eV). Eulytite glasses were obtained from Bi4GeO14 sintered powder or mixture oxides powders Bi2O3-GeO2. The powders rapidly heated and melted at 1050 degrees C for 5 divided by 10 min was poured on the graphite plates under the glass transition temperature. Structural SEM, XRD and EDX investigations were performed at room temperatures. The frequency dependence of the permittivity and loss (45 Hz divided by 5 MHz) was investigated on a large temperature range between -140 and +375 degrees C. The permittivity and loss increase with the temperatures increase and decrease with the frequency increase. An activation energy of 0.88 kcal/mol, comparable to the thermal energy RT = 0.65 kcal/mol, was found for cluster formation on 150 divided by 200 degrees C temperature range. The jump of permittivity on the range 275 divided by 325 degrees C suggest an incipient glass transition at lower temperatures than 400 degrees C, as usually is accepted. The permittivity increase, correlated with the dipolar polarization was noticed at higher temperatures. The decrease of permittivity and loss in 10 divided by 100 kHz frequency range, at the mentioned temperatures, supports this assertion. The estimated relaxation times suggest the big clusters formation. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Bi-4(GeO4)(3) glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408 K (135 degrees C) and 610 K (337 degrees C). The differences between the Bi-4(GeO4)(3) crystals and glass materials are believed to result from the random distribution of GeO4 tetrahedra around Bi3+ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600 degrees C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency. (C) 2010 Elsevier Ltd. All rights reserved.

New nano-configuration has been modelled, based on nano-tubes of carbon and arsenic sulphide. The properties of this complex structure have been analysed. The modelling shows that the construction of composite nano-structures in different nano-systems are possible.

The thermal spike model which takes into account both ionization and nuclear energy loss processes of the projectile as distinct electronic and atomic heat sources is used to describe transient processes induced by ions in silicon. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated. The contribution of the rise in temperature on defect formation and annealing is considered.

Iron/iron oxide-based nanocomposites were prepared by IR laser sensitized pyrolysis of Fe(CO)(5) and methylmethacrylate (MMA) mixtures. The morphology of nanopowder analyzed by TEM indicated that mainly core-shell structures were obtained. X-ray diffraction techniques evidence the cores as formedmainly by iron/iron oxide crystalline phases. A partially degraded (carbonized) polymeric matrix is suggested for the coverage of the metallic particles. The nanocomposite structure at the variation of the laser density and of the MMA flow was studied. The new materials prepared as thick films were tested for their potential for acting as gas sensors. The temporal variation of the electrical resistance in presence of NO2, CO, and CO2, in dry and humid air was recorded. Preliminary results show that the samples obtained at higher laser power density exhibit rather high sensitivity towards NO2 detection and NO2 selectivity relatively to CO and CO2. An optimum working temperature of 200 degrees C was found.

Electrochemical replication of nanoporous membranes represents a facile approach towards the fabrication of nanostructures with tailored properties. By the template method we prepared multisegment nanowires with tailored structure. The first step of the process was the fabrication of the nanoporous template by swift heavy ion irradiation and subsequent selective etching of the ion track. The next step was to fill the pores with the desired combination of materials. In this manner, by sequential electrodeposition steps of metal and semiconductor we prepared Ni - CdTe and Ni - ZnO - Ni nanowires.

Barium stearate multilayer samples have been deposited by the Langmuir-Blodgett technique. Carbon nanotubes have been added in the deposition solution. The structural properties have been studied. The effect of the doped multilayers has been tested against the solution of ammonium nitrate in water. The effect of (5,10,15,20-tetraphenyl)-porphinato manganese (III) chloride, (MnTPP)Cl, on the multilayer sample has been tested. The change of resistivity of the multilayer samples modified by manganese porphyrin, as a function of the ultraviolet radiation has been discovered and investigated. The increase of the resistance during irradiation is a reversible process, although a slow one. This effect could give a basis for applications in UV sensors and switches. Finally, a photo-resistive effect (induced by UV light) has been discovered in Barium stearate layers doped by silver nitrate.

CuIn1-xGaxS2 (CIGS2) thin-films for solar cells were prepared by rf-magnetron sputtering and were deposited on glass substrate. These films were prepared using a stepwise process consisting of succesive deposition of CuInGa (d = 1500 nm) and ZnS (d = 200 nm) layers. Each layer was structurally characterized by X-ray diffraction and atomic force microscopy. The microstructural and optical properties of CIGS2 component films of the solar cell in comparison with those of ZnS and CuInGa films separately deposited onto glass substrates under the same conditions, were studied. Transmission spectra of our thin films are strongly influenced by deposition conditions and nature of the support material and they were recorded for each component film and CIGS2 solar cell.

The relaxation of the irreversible magnetization in optimally doped YBCO films with natural and artificial pinning centres was measured in zero-field cooling conditions using SQUID magnetometry. The external magnetic field H was oriented along the c axis. An appropriate method for the determination of the characteristic vortex pinning energy from the normalized vortex-creep activation energy is discussed. This is based on the existence of a crossover elastic (collective) vortex creep at low temperatures T - plastic vortex creep at high T, caused by the T dependent macroscopic currents induced in the sample during magnetization measurements.

Bioceramic composites were obtained by combining two biocompatible components (by example- in our studies - hydroxyapatite and iron oxide nanoparticles). The preparation method determines the particle size and shape, the size distribution, the surface chemistry of the iron oxide particles and consequently their magnetic properties. The samples were analysed by X-ray diffraction and IR spectroscopy. Their thermal behaviour was studied by thermogravimetric and thermodifferential analysis. These characterization techniques confirmed the presence of hydroxyapatite on the magnetite surface. Osteoblast cell cultures were used to determine cell proliferation, viability and cytotoxicity on interaction with the samples. The cultures displayed good in vitro behaviour.